Optical pickup and disc drive device

ABSTRACT

An objective lens driving device is to be improved in sensitivity and reduced in size and thickness. To this end, an objective lens driving device includes a stationary block arranged on a stationary plate provided on a movable base, a movable block holding an objective lens and moved along the focusing direction, the tracking direction and the tilt direction, support springs for supporting the movable block with respect to the stationary block, a first magnetic circuit for causing movement of the movable block along the focusing direction and along the tracking direction, and a second magnetic circuit for causing movement of the movable block along the tilt direction. The second magnetic circuit includes a pair of tilt magnets, each having two poles so that N poles and S poles lie along the tangential direction, and a pair of tilt coils facing the tilt magnets and each having an axis of winding wire direction along the tangential direction. The tilt magnets and the tilt coils are mounted to the movable block and the stationary block, respectively. An objective lens and the second magnetic circuit are arranged on the opposite sides along the tangential direction with the first magnetic circuit in-between.

CROSS REFERENCES TO RELATED APPLICATIONS

The present invention contains subject matter related to Japanese PatentApplication JP 2004-117647 filed in the Japanese Patent Office on Apr.13, 2004, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an optical pickup and a disc drive device.More particularly, it relates to an optical pickup having a drivingdevice for an objective lens in which a movable block is moved in thethree directions of focusing, tracking and tilt with respect to astationary block and to a disc drive device having the optical pickup.

2. Description of Related Art

The disc drive device records and/or reproduces information signals fora disc-shaped recording medium, such as an optical disc. This disc drivedevice is provided with an optical pickup that is moved radially of thedisc-shaped recording medium for illuminating laser light thereon.

The optical pickup is provided with an objective lens driving device,and by this objective lens driving device, the objective lens held bythe movable block is moved along the focusing direction or is movedalong the tracking direction, in order to condense the spot of the laserlight illuminated via the objective lens on the disc-shaped recordingmedium on a recoding track thereof. The focusing direction is thedirection along which the objective lens held by the movable block ofthe objective lens driving device is moved towards and away from therecording surface of the disc-shaped recording medium by way of afocusing adjustment, and the tracking direction is substantially theradial direction of the disc-shaped recording medium along which theobjective lens is moved for tracking adjustment.

The practice in the optical pickup has been to effect focusingadjustment and tracking adjustment by the objective lens driving device.Recently, there has been developed an objective lens driving device,also called a tri-axial actuator, which enables an adjustment forsurface plane deviation of the rotating disc-shaped recording medium byallowing a movable block to be tilted relative to the recording surfaceof the disc-shaped recording medium in addition to a biaxial adjustmentof a focusing adjustment and a tracking adjustment, for improving thefollow-up characteristics of the laser light spot with respect to therecording track. Thus, with the objective lens driving device, called atri-axial actuator, the movable block is moved along the focusingdirection, the tracking direction and a tilt direction which is adirection about an axis extending along the tangential directionperpendicular to the radial direction of the disc-shaped recordingmedium.

As the objective lens driving device, called the tri-axial actuator, thefollowing type devices have been developed so far.

For example, a movable block holding an objective lens is movablycarried on a stationary block via a support spring, a tilt coil fortilting the movable block relative to the stationary block is providedto the movable block, and a tilt magnet positioned facing the tilt coilis provided to the stationary block. The device type in which the tiltcoil is provided to the movable block is termed a moving-coil-typedevice.

With the moving-coil-type objective lens driving device, two supportsprings each are needed for supplying driving currents to the focusingcoils for focusing adjustment, the tracking coils for trackingadjustment and the tilt coil for tilt adjustment provided to the movableblock side, such that the movable block is carried by the stationaryblock with a sum total of six support springs.

On the other hand, with a tri-axial actuator, which is of the typedifferent from the moving-coil-type device, the movable block holdingthe objective lens is movably supported by the stationary block viasupport springs, while a tilt coil for tilting the movable blockrelative to the stationary block is provided to the stationary block,and a tilt magnet positioned facing the tilt coil is provided to themovable block (see, for example, the Patent Publication 1 (JapaneseLaid-Open Patent Publication 2000-222755)). The device type in which thetilt magnet is provided to the movable block is called amoving-magnet-type device.

With the moving-magnet-type objective lens driving device, in which thetilt magnet is provided to the movable block, the weight of the movableblock becomes larger than that of the moving-coil-type device. However,the moving-magnet-type device does not need a support spring forsupplying the driving current to the tilt coil and hence is meritoriouswhen compared to the moving-coil-type device, in that the number ofcomponent parts may be reduced and in that the assembly operation can befacilitated.

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

With the objective lens driving device described in patent Publication1, the tilt magnet provided to the movable block has a single N pole anda single S pole, while the tilt coil provided to the stationary blockhas the winding core direction corresponding to the focusing direction,and hence the movable block is moved along the tilt direction undercooperation between the driving current flowing in about one-fourth partof the tilt coil wound in the from of a square tube and the magneticflux of the magnet. Consequently, the portion of the tilt coil used fortilt adjustment is small, and hence the device may be lowered insensitivity.

For combating the decrease in sensitivity, it becomes necessary to use amagnet of a high magnetic force or to supply a large driving current tothe tilt coil. However, this raises the manufacturing cost or powerconsumption of the objective lens driving device.

Moreover, should the tilt coil be arranged so that the winding coredirection corresponds to the focusing direction, the space in which tomount the tilt coil along the tangential direction is correspondinglyincreased and the objective lens driving device is increased in sizealong the tangential direction in a manner deterrent to size reduction.In addition, the supporting state of the movable block tends to beunstable.

With the objective lens driving device, the laser light radiated from alight source is conducted to the objective lens via an uplift mirrorarranged on the opposite side of the disc-shaped recording medium withthe movable block in-between. If in such case a magnetic circuit formedby, for example, a coil or a magnet is arranged about the objectivelens, the optical path of the laser light radiated from the light sourceso as to be incident on the uplift mirror needs to be provided below themagnetic circuit, with the result that the objective lens driving deviceis increased in thickness, contrary to the demand for reducing itsthickness. In particular, in an optical pickup provided to a device fora mobile phone, in which there is raised a high demand for a reductionin thickness, deterrence of the reduction in thickness is a majorproblem.

To overcome the above problem, it is desirable to provide an objectivelens driving device that may be improved in sensitivity and reduced insize and thickness.

Means to Solve the Problem

For accomplishing the above problem, the present invention provides anoptical pickup and a disc drive device in which an objective lensdriving device includes a stationary plate provided on the movable base;a stationary block arranged on the stationary plate and secured to themovable base; a movable block for holding the objective lens andoperated relative to the stationary block along a focusing direction,which is a direction towards and away from a recording surface of thedisc-shaped recording medium, along a tracking direction, which is aradial direction of the disc-shaped recording medium, and along a tiltdirection which is a direction about an axis extending along thetangential direction perpendicular to the radial direction of thedisc-shaped recording medium; a plurality of support springs for movablysupporting the movable block relative to the stationary block; a firstmagnetic circuit for causing movement of the movable block along thefocusing direction or along the tracking direction; and a secondmagnetic circuit for causing movement of the movable block along thetilt direction. The second magnetic circuit includes a pair of tiltmagnets each magnetized to two poles so that N and S poles are arrangedalong the focusing direction. The paired tilt magnets are spaced apartfrom each other along the radial direction. The second magnetic circuitalso includes a pair of tilt coils arranged facing the paired tiltmagnets, with each of the tilt coils having an axis of the winding wiredirection corresponding to the tangential direction. The paired tiltmagnets are provided to the movable block, the paired tilt coils areprovided to the stationary block, while the objective lens and thesecond magnetic circuit are located on both sides of the first magneticcircuit along the tangential direction.

Hence, with the optical pickup and the disc drive device, according tothe present invention, the portion of the tilt coil usable for tiltadjustment may be increased.

The present invention also provides an optical pickup including amovable base moved along the radial direction of a disc-shaped recordingmedium loaded on a disc table and an objective lens driving devicearranged on the movable base. The objective lens driving devicecomprises a stationary plate provided on the movable base; a stationaryblock arranged on the stationary plate and secured to the movable base;a movable block for holding the objective lens operated relative to thestationary block along a focusing direction, which is a directiontowards and away from a recording surface of the disc-shaped recordingmedium, along a tracking direction, which is a radial direction of thedisc-shaped recording medium, and along a tilt direction, which is adirection about an axis extending along the tangential directionperpendicular to the radial direction of the disc-shaped recordingmedium; a plurality of support springs for movably supporting themovable block relative to the stationary block; a first magnetic circuitfor causing movement of the movable block along the focusing directionor along the tracking direction; and a second magnetic circuit forcausing movement of the movable block along the tilt direction. Thesecond magnetic circuit includes a pair of tilt magnets each magnetizedto two poles so that N and S poles are arranged along the focusingdirection. The paired tilt magnets are spaced apart from each otheralong the radial direction. The second magnetic circuit also includes apair of tilt coils arranged facing the paired tilt magnets and eachhaving an axis of the winding wire direction corresponding to thetangential direction. The paired tilt magnets are provided to themovable block, while the paired tilt coils are provided to thestationary block. The objective lens and the second magnetic circuit arelocated on both sides of the first magnetic circuit along the tangentialdirection.

Since the tilt coils are arranged with the winding core directionextending along the tangential direction, the portion of the tilt coilsusable for generating the force of thrust in the movable block along thetilt direction may be increased to improve the sensitivity of themovable block at the time of tilt adjustment.

Moreover, since the movable block may be improved in sensitivity, it isunnecessary to use the magnet with a stronger magnetic force, while thedriving current supplied to the tilt coils may be smaller, with theresult that the power consumption as well as the manufacture costs ofthe objective lens driving device may be lowered.

Additionally, since the winding core direction of the tilt coils is notthe focusing direction, the tilt coil mounting space along thetangential direction may be smaller, and hence the size of the objectivelens driving device along the tangential direction may be reduced.

Since the objective lens and the second magnetic circuit are arranged onopposite sides along the tangential direction with the first magneticcircuit in-between, the uplift mirror may be provided at the same heightlevel as the first magnetic circuit, and hence the objective lensdriving device may be correspondingly reduced in thickness. Thisreduction in thickness is particularly desirable in an optical pickupused for mobile equipment.

Furthermore, since the tilt magnets and the tilt coils are provided tothe movable block and to the stationary block, respectively, the supportsprings for supplying the current to the tilt coils may be dispensedwith, thereby reducing the number of component parts and simplifying theassembling performance of the objective lens driving device.

Since there is provided a tilt yoke by bending a portion of thestationary plate on the opposite side of the tilt magnet along thetangential direction with the tilt coil in-between, there is no need toprovide dedicated separate tilt yokes, while the portion for securingthe stationary block and the tilt yokes may be used in common, thusreducing the number of component parts. Since a back yoke is provided onthe surface of the tilt magnet opposite to the surface thereof facingthe tilt coil, it is possible to improve the sensitivity of the movableblock at the time of tilt adjustment.

Additionally, the stray magnetic flux from the tilt magnets may bereduced, and the second magnetic circuit does not tend to be affected bythe first magnetic circuit, while the movable block may be preventedfrom being tilted relative to the stationary block under the effect ofthe stray magnetic flux.

The present invention also provides a disc drive device comprising adisc table for loading a disc-shaped recording medium thereon and anoptical pickup for radiating laser light via an objective lens to thedisc-shaped recording medium loaded on the disc table. The opticalpickup includes a movable base, moved along the radial direction of adisc-shaped recording medium, and loaded on a disc table, and anobjective lens driving device arranged on the movable base. Theobjective lens driving device includes a stationary plate provided onthe movable base; a stationary block arranged on the stationary plateand secured to the movable base; and a movable block for holding theobjective lens and operated relative to the stationary block along afocusing direction, which is a direction towards and away from arecording surface of the disc-shaped recording medium, along a trackingdirection, which is a radial direction of the disc-shaped recordingmedium, and along a tilt direction, which is a direction about an axisextending along the tangential direction perpendicular to the radialdirection of the disc-shaped recording medium. The objective lensdriving device includes a plurality of support springs for movablysupporting the movable block relative to the stationary block, a firstmagnetic circuit for causing movement of the movable block along thefocusing direction or along the tracking direction, and a secondmagnetic circuit for causing movement of the movable block along thetilt direction. The second magnetic circuit includes a pair of tiltmagnets each magnetized to two poles so that N and S poles are arrangedalong the focusing direction, with the paired tilt magnets being spacedapart from each other along the radial direction. The second magneticcircuit also includes a pair of tilt coils arranged facing the pairedtilt magnets, each of the tilt coils having an axis of the winding wiredirection corresponding to the tangential direction. The paired tiltmagnets are provided to the movable block, and the paired tilt coils areprovided to the stationary block. The objective lens and the secondmagnetic circuit are located on both sides of the first magnetic circuitalong the tangential direction.

Since the tilt coils are arranged with the winding core directioncorresponding to the tangential direction, the portion of the tilt coilsusable for generating the force of thrust in the movable block along thetilt direction is larger, thus improving the sensitivity of the movableblock at the time of tilt adjustment.

Moreover, since the movable block may be improved in sensitivity, it isunnecessary to use the magnet with a stronger magnetic force, while thedriving current supplied to the tilt coils may be reduced, with theresult that the power consumption as well as the manufacturing costs ofthe objective lens driving device may be lowered.

Additionally, since the winding core direction of the tilt coils is notthe focusing direction, the tilt coil mounting space along thetangential direction may be smaller, and hence the size of the objectivelens driving device along the tangential direction may be reduced.

Since the objective lens and the second magnetic circuit are arranged onopposite sides along the tangential direction with the first magneticcircuit in-between, the uplift mirror may be provided at the same heightlevel as the first magnetic circuit, and hence the objective lensdriving device may be correspondingly reduced in thickness. Thisreduction in thickness is particularly desirable in an optical pickupused for mobile equipment.

In addition, since the tilt magnets and the tilt coils are provided tothe movable block and the stationary block, respectively, the supportsprings for supplying the current to the tilt coils may be dispensedwith, thereby reducing the number of component parts and simplifying theassembling performance of the objective lens driving device.

Since a tilt yoke is provided by bending a portion of the stationaryplate on the opposite side of the tilt magnet along the tangentialdirection with the tilt coil in-between, there is no need to providededicated separate tilt yokes, while the portion for securing thestationary block and the tilt yokes may be used in common, thus reducingthe number of component parts.

Since a back yoke is provided on the surface of the tilt magnet oppositeto the surface thereof facing the tilt coil, it is possible to improvethe sensitivity of the movable block at the time of tilt adjustment.

Additonally, the stray magnetic flux from the tilt magnets may bereduced, and the second magnetic circuit is not liable to be affected bythe first magnetic circuit, while the movable block may be preventedfrom being tilted relative to the stationary block under the effect ofthe stray magnetic flux.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows, in conjunction with FIGS. 2 and 12, the best mode ofcarrying out the present invention and, specifically, is a schematiccross-sectional view of a disc drive device of the present invention.

FIG. 2 is a partially-exploded, enlarged perspective view showing aportion of an objective lens driving device.

FIG. 3 is an enlarged perspective view of the objective lens drivingdevice.

FIG. 4 is an enlarged perspective view showing the objective lensdriving device from which a power feed base plate has been detached.

FIG. 5 is an enlarged perspective view showing the objective lensdriving device, as viewed from a direction different from the viewingdirection of FIG. 3.

FIG. 6 is an enlarged exploded perspective view showing a stationaryblock.

FIG. 7 is an enlarged perspective view showing the objective lensdriving device, as viewed from a direction different from the viewingdirections of FIGS. 3 and 5, with a portion thereof being removed.

FIG. 8 is an enlarged perspective view showing a first magnetic circuitand a second magnetic circuit.

FIG. 9 is a schematic enlarged side view showing an objective lensdriving device.

FIG. 10 is a schematic view showing the direction of the magnetic forcein the case where there is provided no back yoke.

FIG. 11 is a schematic view for illustrating the operation which mayoccur in the case where there is provided no back yoke.

FIG. 12 is a schematic view showing the direction of the magnetic forcein the case where there is provided a back yoke.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The best mode of an optical pickup and a disc drive device according tothe present invention is now explained with reference to the drawings.

The disc drive device 1 includes respective components and units in anouter casing 2, as shown in FIG. 1. In the outer casing is formed a discentrance opening, not shown. Within the outer casing 2, there is mounteda chassis, not shown. A disc table 3 is secured to a motor shaft of aspindle motor mounted on the chassis.

On the chassis, there are mounted guide shafts 4, 4 for extendingparallel to each other and a lead screw 5 rotated by a feed screw, notshown.

An optical pickup 6 includes a movable base 7, optical componentsprovided on the movable base 7, and an objective lens driving device 8arranged on the movable base 7. The ends of the movable base 7 arefitted with bearings 7 a, 7 b, which are slidably supported by the guideshafts 4, 4.

A nut member, not shown, is provided on the movable base 7. When thelead screw 5 is rotated by a feed motor, the nut member is fed in adirection consistent with the direction of rotation of the lead screw 5,such that the optical pickup 6 is moved along the radial direction of adisc-shaped recording medium 100 that is to be loaded on the disc table3.

The objective lens driving device 8 includes a base member 9, astationary plate 10, a stationary block 11 and a movable block 12operated relative to the stationary block 11 (see FIGS. 2 and 3).

The base member 9 is formed of, for example, SPCC (cold rolled stainlesssteel sheet) or a silicon steel sheet and, as shown in FIG. 2, made upby a base part 9 a secured to the movable base 7 and yoke parts 9 b, 9 bbent from the base part 9 a perpendicularly thereto. The yoke parts 9 b,9 b are provided spaced apart from each other in the fore-and-aftdirection, that is, in the tangential direction (TA) of the disc-shapedrecording medium 100.

The surfaces of the yokes 9 b, 9 b facing each other are fitted withmagnets 13, 13.

The stationary plate 10 is provided spaced apart along the tangentialdirection (towards rear) with respect to the base member 9 and securedto the movable base 7. The stationary plate 10 is formed by a sheet of amagnetic metal material, for example, SPCC (cold rolled stainless steel)or a silicon steel and made up by a plate base 10 a secured to themovable base 7 and tilt yokes 10 b, 10 c, bent from a forward end partof the base plate 10 a and spaced apart from each other along the radialdirection (RAD) of the disc-shaped recording medium 100.

The stationary block 11 is secured to the plate base 10 a of thestationary plate 10. On the left and right ends of the back surface ofthe stationary block 11, there are provided a sum total of fourterminals 11 a, 11 a, . . . in a vertically-spaced apart relationrelative to each other, as shown in FIGS. 4 and 5.

The lower end of the stationary block 11 is provided with terminal pins11 b, 11 b protruded towards the rear from the back surface thereof (seeFIG. 4). These terminal pins 11 b, 11 b are located spaced apart in theleft and right directions.

On the forward surface of the stationary block 11, there are formedforwardly protruded positioning lugs 11 c, 11 c spaced apart from eachother in the left and right directions (see FIG. 6).

On the rear surface of the stationary block 11 is mounted a relaysubstrate 14 (see FIG. 4). The relay substrate 14 is made up by a basicpart 14 a and four connecting parts 14 b, 14 b, . . . protruded in theleft and right directions from the basic part 14 a. The foremost partsof the connecting parts 14 b, 14 b, . . . of the relay substrate 14 areconnected with, for example, solders 15, 15, . . . to the terminals 11a, 11 a, . . . respectively.

A pair of tilt coils 16, 16 are mounted to the front surface of thestationary block 11 on the left and right sides thereof, that is, thetilt coils are spaced apart along the radial direction of thedisc-shaped recording medium 100 (see FIGS. 3 and 6). These tilt coils16, 16 are mounted to the stationary block 11 by being fitted onpositioning lugs 11 c, 11 c provided on the front surface of thestationary block 11. Thus, by providing the positioning lugs 11 c, 11 cto the stationary block 11, the tilt coils 16, 16 may readily be mountedin position to the stationary block 11.

The tilt coils 16, 16 are formed substantially to a square tubular shapewith a thin wall thickness and mounted to the stationary block 11 sothat the direction of winding cores thereof coincides with thefore-and-aft direction, that is, with the aforementioned tangentialdirection. The tilt coils 16, 16 are provided with upper and lowerportions 16 a, 16 a, . . . operating for generating the force of thrustin the movable block 12 along the tilt direction. Meanwhile, the tiltdirection is the direction of deviation of the plane of the disc-shapedrecording medium 100 from its intended plane (direction indicated by Rin FIG. 3), that is, the direction of rotation of the disc-shapedrecording medium about an axis extending along the tangential direction.

One end of the tilt coils 16, 16 is mounted by being coiled about theterminal pins 11 b, 11 b provided to the back surface of the stationaryblock 11 (see FIG. 4).

To the relay substrate 14 mounted to the back surface of the stationaryblock 11, there is fixedly connected a substrate for power supply 17,connected in turn to a power supply circuit, not shown (see FIGS. 4 and5). The substrate for power supply 17 is, for example, a flexibleprinted circuit board and includes four connecting parts (lines) 17 a,17 a, . . . and two connecting parts (lines) 17 b, 17 b. The connectinglines 17 a, 17 a, . . . are connected by, for example, solders 18, 18, .. . to the connecting lines 14 b, 14 b, . . . of the relay substrate 14,respectively, while the connecting lines 17 b, 17 b are connected by,for example, solders 19, 19 to one end of the tilt coils 16, 16 mountedto the terminal pins 11 b, 11 b. Thus, the driving current for tiltadjustment is supplied to the tilt coils 16, 16 from a power supplycircuit via connecting lines 17 b, 17 b of the substrate for powersupply 17.

In this manner, one end of the tilt coils 16, 16 is coiled around theterminal pins 11 b, 11 b, and the one end of the tilt coils 16, 16 issecured to the connecting lines 17 b, 17 b by the solders 19, 19, andhence the substrate for power supply 17 can be secured to the tilt coils16, 16 extremely readily, thus simplifying the operation of connectingthe substrate for power supply 17 to the tilt coils 16, 16 and improvingthe connection reliability.

Towards the forward end of the stationary block 11 are formedvertically-extending openings for yokes 11 d, 11 d (see FIGS. 6 and 7)within which are arranged tilt yokes 10 b, 10 b of the stationary plate10 introduced from below. The tilt yokes 10 b, 10 b are arrangeddirectly in rear of the tilt coils 16, 16.

To the terminals 11 a, 11 a, . . . of the stationary block 11 areattached the rear ends of support springs 20, 20, . . . (see FIGS. 3 and4). These support springs 20, 20, . . . are connected via terminals 11a, 11 a, . . . and connecting parts 14 b, 14 b, . . . of the relaysubstrate 14 to the connecting lines 17 a, 17 a, . . . of the substratefor power supply 17. The support springs 20, 20, . . . are protrudedforward from the stationary block 11.

The movable block 12 includes a movable holder 21 and an objective lens22 held thereby (see FIGS. 3 to 5).

The movable holder 21 is formed as one with a lens mounting unit 23 anda coil holder 24 mounted to the rear side of the lens mounting unit 23.

The lens mounting unit 23 is formed with a vertically extendingthrough-opening 23 a (see FIG. 7), and the objective lens 22 is mountedoverlying the through-opening 23 a.

The coil holder 24 is formed as a vertically perforated substantiallyrectangular frame, and a focusing coil 25 and a pair of tracking coils26, 26 are held in the inside of the coil holder 24 formed onperforation.

The focusing coil 25 is used for causing movement of the movable block12 along the focusing direction, that is, in the direction towards andaway from the disc-shaped recording medium 100 (direction F in FIG. 3).The tracking coils 26, 26 are used for causing movement of the movableblock 12 along the tracking direction, that is, in the directionsubstantially along the radius of the disc-shaped recording medium 100(direction T in FIG. 3).

The focusing coil 25 and the tracking coils 26, 26 are each in the formof a substantially square-shaped tube, with the focusing coil 25 havinga winding core extending in the up-and-down direction (focusingdirection), and with the tracking coils 26, 26 having winding coresextending in the fore-and-aft direction (tangential direction). Thetracking coils 26, 26 are provided spaced apart from each other on thefront side of the focusing coil 25.

The ends of the focusing coil 25 and the tracking coils 26, 26 areconnected to connection terminals 21 a, 21 a, . . . provided on bothlateral sides of the movable holder 21. To the connection terminals 21a, 21 a, . . . are connected forward ends of the support springs 20, 20,. . . . Hence, the movable block 12 is connected by the support springs20, 20, . . . and maintained in the hollow state.

If, in the objective lens driving device 8, the movable block 12 ismaintained in the hollow state relative to the stationary block 11 bythe support springs 20, 20, . . . , as described above, and the movableblock 12 is moved in a direction in which the focusing direction is theup-and-down direction, the movable block 12 is moved downwards under itsown gravity and the support springs 20, 20, . . . become flexed suchthat the forward ends of the support springs 20, 20, . . . are at alower position than the rear ends thereof. With the objective lensdriving device 8, the position thereof in which the movable block 12 ismoved downwards under its own weight is set as a neutral position alongthe focusing direction of the movable block 12. Thus, in the neutralposition along the focusing direction, the center in the up-and-downdirection of tilt magnets 29, 29, that is, the neutral line M1 betweenthe magnetic poles, coincides with the center M2 in the up-and-downdirection of the tilt coils 16, 16.

By setting the position of the movable block 12, which has taken its owngravity into account, as the neutral position thereof along the focusingdirection, variations in tilt characteristics of the movable block 12attendant on the focusing movements become symmetrical in theup-and-down direction, thereby assuring reliability in the tiltmovements of the objective lens driving device 8.

Meanwhile, in case the objective lens driving device 8 is used in astate in which the focusing direction is not the up-and-down direction,it is sufficient if the position of the movable block 12 when thedriving current supplied to the focusing coil 25 as the focusing servois applied to the movable block 12 is zero is set as the neutralposition of the movable block 12 along the focusing direction.

The support springs 20, 20, . . . are supplied from a power supplycircuit with driving currents for focusing adjustment or for trackingadjustment via connecting lines 17 a, 17 a, . . . of the substrate forpower supply 17 and via connecting parts 14 b, 14 b, . . . of the relaysubstrate 14. Thus, two each of the support springs 20, 20, . . .operate as power supply members for supplying power to the focusing coil25 and the tracking coils 26, 26.

The forward sides of the focusing coil 25 and both the forward and rearsides of the tracking coils 26, 26 are associated with a pair of magnets13, 13, secured to the yoke parts 9 b, 9 b (see FIG. 8). By arrangingthe magnets 13, 13 in this manner, a first magnetic circuit 27 forcausing movement of the movable block 12 in the focusing direction or inthe tracking direction is formed by the magnets 13, 13, yoke parts 9 b,9 b, focusing coil 25 and the tracking coils 26, 26.

On the rear side upper surface of the coil holder 24 of the movableholder 21, there are mounted back yokes 28, 28 and the tilt magnets 29,29 in vertically stacked states, with the back yokes being spaced apartfrom the magnets in the left and right direction (see FIGS. 2 and 3).The tilt magnets 29, 29 are magnetized to N poles 29 a, 29 a and S poles29 b, 29 b separated from the N poles along the focusing direction, asshown in FIG. 2.

The tilt magnets 29, 29 are positioned facing the tilt coils 16, 16mounted on the forward surface of the stationary block 11 (see FIG. 8).With the tilt magnets 29, 29 positioned facing the tilt coils 16, 16 inthis manner, a second magnetic circuit 30 for causing movement of themovable block 12 along the tilt direction is formed by the tilt magnets29, 29, back yokes 28, 28, tilt coils 16, 16 and the tilt yokes 10 b, 10b.

When the driving current is supplied to the focusing coil 25 or to thetracking coils 26, 26 from the power supply circuit through thesubstrate for power supply 17, the relay substrate 14 and the supportsprings 20, 20, . . . , the movable block 12 is moved in the focusingdirection (direction F in FIG. 3) or in the tracking direction(direction T in FIG. 3), depending on the relationship between thedirection of the driving current and the direction of the magnetic fluxgenerated in the magnets 13, 13 and the yoke parts 9 b, 9 b.

Moreover, when the driving current is supplied from the power supplycircuit through the substrate for power supply 17 to the tilt coils 16,16, the movable block 12 is moved in the tilt direction (direction R inFIG. 3) by the relationship between the direction of the driving currentand the direction of the magnetic flux generated in the back yokes 28,28 and the tilt magnets 29, 29 and the tilt yokes 10 b, 10 b. It isnoted that tilt adjustment is effected by the movable block 12 beingmoved along the tilt direction by the force of thrust generated inopposite directions (up-and-down direction) on the left and right sidesof the movable block in case the driving current is supplied to the tiltcoils 16, 16.

When the movable block 12 is moved in the focusing direction, thetracking direction or in the tilt direction, the support springs 20, 20are elastically deformed.

An uplift mirror 31 is arranged below the objective lens 22 mounted tothe movable holder 21 (see FIG. 9).

In the above-described disc drive device 1, if the disc table 3 is runin rotation with the rotation of a spindle motor, not shown, thedisc-shaped recording medium 100, mounted on the disc table 3 is run inrotation at the same time as the optical pickup 6 is moved along theradius of the disc-shaped recording medium 100, by way of recordingand/or reproducing the disc-shaped recording medium 100.

If, during this recording and/or reproducing operation, the drivingcurrent is supplied to the focusing coil 25, the movable block 12 of theobjective lens driving device 8 is moved along the focusing directionF-F in FIG. 3 relative to the stationary block 11, so that the lightspot of laser light radiated from a light source, not shown, andilluminated via objective lens 22 is condensed substantially vertically,in order to cope with the warping of the disc-shaped recording medium100, by way of performing the focusing adjustment.

When the driving current is supplied to the tracking coils 26, 26, themovable block 12 of the objective lens driving device 8 is moved alongthe tracking direction T-T, shown in FIG. 3, relative to the stationaryblock 11, so that the light spot of laser light radiated from the lightsource and illuminated via the objective lens 22 is condensed on arecording track of the disc-shaped recording medium 100, by way ofperforming the tracking adjustment.

When the driving current is supplied to the tilt coils 16, 16, themovable block 12 of the objective lens driving device 8 is moved alongthe tilt direction R-R, shown in FIG. 3, with respect to the stationaryblock 11, such that the spot of the laser light radiated from the lightsource and illuminated via objective lens 22 is condensed on therecording track of the disc-shaped recording medium 100, by way ofperforming tilt adjustment.

With the optical pickup 6, described above, in which there are providedthe tilt magnets 29, 29 having N poles 29 a, 29 a and S poles 29 b, 29 bseparated from the N poles along the focusing direction, and in whichthe direction of the winding cores of the tilt coils 16, 16 is thetangential direction, about one-half portions 16 a, 16 a, . . . of theentire tilt coils 16, 16 may be used as portions responsible forproducing the force of thrust along the tilt direction in the movableblock 12, thereby improving the sensitivity of the movable block 12 atthe time of tilt adjustment.

Since the movable block 12 may be improved in sensitivity, there is noneed to use magnets with correspondingly strong magnetic force, whilethere is also no necessity for supplying high driving current to thetilt coils 16, 16, thereby reducing manufacturing costs of the objectivelens driving device 8 and power consumption.

Additionally, since the direction of the winding cores of the tilt coils16, 16 is not the focusing direction, a small mounting space for thetilt coils 16, 16 along the tangential direction suffices, with theresult that the size of the objective lens driving device along thetangential direction may be reduced.

Moreover, with the objective lens driving device 8, in which theobjective lens 22 and the second magnetic circuit 30 for tilt adjustmentare arranged on opposite sides along the tangential direction of thefirst magnetic circuit 27 responsible for focusing adjustment andtracking adjustment, the uplift mirror 31 may be of the same heightlevel as the first magnetic circuit 27, and hence the objective lensdriving device 8 may correspondingly be reduced in thickness. Thisreduction in thickness is particularly suitable for an optical pickupused for a portable apparatus.

With the objective lens driving device 8 in which the tilt magnets 29,29 are provided to the movable block 12 and the tilt coils 16, 16 areprovided to the stationary block 11, there is no necessity for providinga support spring for supplying the power to the tilt coils 16, 16, withthe result that the number of component parts may correspondingly bereduced to simplify the assembly process for the objective lens drivingdevice 8.

In addition, with the objective lens driving device 8 in which thestationary plate 10 for securing the stationary block 11 is bent to formthe tilt yokes 10 b, 10 b there is no need to provide dedicated tiltyokes, and the plate base 10 a and the tilt yokes 10 b, 10 b, ascomponents for securing the stationary block 11, may be used in common,with the consequence that the number of component parts may be reducedfurther.

With the objective lens driving device 8, the back yokes 28, 28 areprovided on the surfaces of the tilt magnets 29, 29 opposite to thesurfaces thereof facing the tilt coils 16, 16.

The result is that the movable block 12 may be improved in sensitivityat the time of tilt adjustment.

Except where the back yokes 28, 28 are provided, the upper portions ofthe tilt magnets 29, 29 are attracted towards the first magnetic circuit27, while the lower portions thereof are repulsed by the first magneticcircuit 27, given the relationship of the directions of the magneticforce produced in relevant parts, as shown in FIG. 10. Hence, the tiltmagnets 29, 29 are subjected to the force of downward movement P, withthe result that the movable block 12 is moved downwards to affect thefocusing operation.

The objective lens driving device 8 is provided with paired tilt magnets29, 29 and paired tilt coils 16, 16 spaced apart from the paired tiltmagnets along the tracking direction (direction T shown in FIG. 11) suchthat, when the movable block 12 has been moved along the trackingdirection by the tracking operation, the positional relationshipsbetween the tilt magnets 29, 29 and the first magnetic circuit 27 arechanged, so that, should the tilt magnets 29, 29 be affected by thefirst magnetic circuit 27, the force of movement acting on the tiltmagnets 29, 29 on the left side differs from that on the right side. Insuch a case, there is the fear that the movable block 12 is tilted inthe direction indicated by R shown in FIG. 11 to tilt the optical axisof the laser light illuminated via objective lens 22 on the disc-shapedrecording medium 100.

Moreover, if in the objective lens driving device 8, the spring force ofthe support springs 20, 20 differs on the left and right sides due tomanufacturing tolerances, the position of the base member 9 along thetracking direction is adjusted in general so that the tilt in theR-direction of the movable block 12 during the focusing movement will beoptimum (zero). In this case, the positional relationships between thetilt magnets 29, 29 and the first magnetic circuit 27 may again bechanged, as above, such that the force of movement acting on the tiltmagnets 29, 29 on the left side differs from that on the right side, andhence the movable block 12 may be tilted in the R-direction shown inFIG. 11.

However, with the objective lens driving device 8 in which the backyokes 28, 28 are provided on the surfaces of the tilt magnets 29, 29opposite to the surfaces thereof facing the tilt coils 16, 16, asdescribed above, the stray magnetic flux from the tilt magnets 29, 29 isdecreased, as shown in FIG. 12, so that the second magnetic circuit 30is not liable to be affected by the first magnetic circuit 27, and henceit is possible to prevent the movable block 12 from being tilted in theR-direction.

The objective lens driving device 8 does not necessarily need to beprovided with the back yokes 28, 28. In such a case, the objective lens22 may be maintained spaced apart from the disc-shaped recording medium100 by taking advantage of the force of movement generated in the tiltmagnets 29, 29 in a direction towards the base member 9 (towards below),in the non-use state in which no driving current is supplied to thefocusing coil 25, without a dependency upon the posture during use ofthe movable block 12, so that the disc-shaped recording medium 100 maybe prevented from contacting with the objective lens 22.

In the foregoing, the focusing and tracking directions are assumed to bethe up-and-down direction and the left and right direction,respectively. This is merely for the sake of illustration so that thepresent invention is not limited to these specific directions.

It should be noted that the particular shape as well as the structure ofrespective parts shown in the best mode for carrying out the inventionis merely exemplary, so that the technical scope of the invention is notto be limited by the merely exemplary shape or structure.

That is, it should be understood by those skilled in the art thatvarious modifications, combinations subcombinations and alterations mayoccur depending on design requirements and other factors insofar as theyare within the scope of the appended claims or the equivalents thereof.

1. An optical pickup having a movable base moved along the radial direction of a disc-shaped recording medium loaded on a disc table; and an objective lens driving device arranged on said movable base, wherein the objective lens driving device comprises: a stationary plate provided on said movable base; a stationary block arranged on said stationary plate and secured to said movable base; a movable block holding said objective lens and operated relative to said stationary block along a focusing direction, which is a direction towards and away from a recording surface of the disc-shaped recording medium, along a tracking direction, which is a radial direction of said disc-shaped recording medium, and along a tilt direction, which is a direction about an axis extending along the tangential direction perpendicular to the radial direction of the disc-shaped recording medium; a plurality of support springs for movably supporting said movable block relative to said stationary block; a first magnetic circuit for causing movement of said movable block along said focusing direction or along said tracking direction; and a second magnetic circuit for causing movement of said movable block along said tilt direction; said second magnetic circuit including a pair of tilt magnets each magnetized to two poles so that N and S poles are arranged along the focusing direction, said paired tilt magnets being spaced apart from each other along said radial direction, and a pair of tilt coils arranged facing said paired tilt magnets, each of said tilt coils having an axis of winding wire direction corresponding to the tangential direction; said paired tilt magnets being provided to said movable block; said paired tilt coils being provided to said stationary block; and said objective lens and the second magnetic circuit being located on both sides of said first magnetic circuit along the tangential direction.
 2. The optical pickup according to claim 1, wherein there is provided a tilt yoke by bending a portion of said stationary plate on the opposite side of said tilt magnet along the tangential direction with said tilt coil in-between.
 3. The optical pickup according to claim 1, wherein a back yoke is provided on the surface of said tilt magnet opposite to the surface thereof facing said tilt coil.
 4. An optical pickup having a movable base moved along the radial direction of a disc-shaped recording medium loaded on a disc table and an objective lens driving device arranged on said movable base, wherein said objective lens driving device comprises: a stationary block secured to said movable base; a movable block holding said objective lens and operated relative to said stationary block along a focusing direction, which is a direction towards and away from a recording surface of the disc-shaped recording medium, along a tracking direction, which is a radial direction of said disc-shaped recording medium, and along a tilt direction, which is a direction about an axis extending along the tangential direction perpendicular to the radial direction of the disc-shaped recording medium; a plurality of support springs for movably supporting said movable block relative to said stationary block; a first magnetic circuit for causing movement of said movable block along said focusing direction or along said tracking direction; and a second magnetic circuit for causing movement of said movable block along said tilt direction; said second magnetic circuit including a pair of tilt magnets each magnetized to two poles so that N and S poles are arranged along the focusing direction, said paired tilt magnets being spaced apart from each other along said radial direction, and a pair of tilt coils arranged facing said paired tilt magnets, each of said tilt coils having an axis of winding wire direction corresponding to the tangential direction; said paired tilt magnets being provided to said movable block; said paired tilt coils being provided to said stationary block; and a back yoke being arranged on the surface of said tilt magnet opposite to the surface thereof facing said tilt coil.
 5. A disc drive device comprising a disc table for loading a disc-shaped recording medium thereon and an optical pickup for radiating laser light via an objective lens to the disc-shaped recording medium loaded on said disc table, said optical pickup including a movable base moved along the radial direction of a disc-shaped recording medium loaded on a disc table, and an objective lens driving device arranged on said movable base, wherein said objective lens driving device comprises: a stationary plate provided on said movable base; a stationary block arranged on said stationary plate and secured to said movable base; a movable block for holding said objective lens and operated relative to said stationary block along a focusing direction, which is a direction towards and away from a recording surface of the disc-shaped recording medium, along a tracking direction, which is a radial direction of said disc-shaped recording medium, and along a tilt direction, which is a direction about an axis extending along the tangential direction perpendicular to the radial direction of the disc-shaped recording medium; a plurality of support springs for movably supporting said movable block relative to said stationary block; a first magnetic circuit for causing movement of said movable block along said focusing direction or along said tracking direction; and a second magnetic circuit for causing movement of said movable block along said tilt direction; said second magnetic circuit including a pair of tilt magnets each magnetized to two poles so that N and S poles are arranged along the focusing direction, said paired tilt magnets being spaced apart from each other along said radial direction, and a pair of tilt coils arranged facing said paired tilt magnets, each of said tilt coils having an axis of winding wire direction corresponding to the tangential direction; said paired tilt magnets being provided to said movable block; said paired tilt coils being provided to said stationary block; and said objective lens and the second magnetic circuit being located on both sides of said first magnetic circuit along the tangential direction.
 6. The disc drive device according to claim 4, wherein there is provided a tilt yoke by bending a portion of said stationary plate on the opposite side of said tilt magnet along the tangential direction with said tilt coil in-between.
 7. The disc drive device according to claim 4, wherein a back yoke is provided on the surface of said tilt magnet opposite to the surface thereof facing said tilt coil.
 8. A disc drive device comprising a disc table for loading a disc-shaped recording medium thereon and an optical pickup for radiating laser light via an objective lens to the disc-shaped recording medium loaded on said disc table, said optical pickup including a movable base moved along the radial direction of a disc-shaped recording medium loaded on a disc table and an objective lens driving device arranged on said movable base wherein said objective lens driving device comprises: a stationary block secured to said movable base; a movable block holding said objective lens and operated relative to said stationary block along a focusing direction, which is a direction towards and away from a recording surface of the disc-shaped recording medium, along a tracking direction, which is a radial direction of said disc-shaped recording medium, and along a tilt direction, which is a direction about an axis extending along the tangential direction perpendicular to the radial direction of the disc-shaped recording medium; a plurality of support springs for movably supporting said movable block relative to said stationary block; a first magnetic circuit for causing movement of said movable block along said focusing direction or along said tracking direction; and a second magnetic circuit for causing movement of said movable block along said tilt direction; said second magnetic circuit including a pair of tilt magnets each magnetized to two poles so that N and S poles are arranged along the focusing direction, said paired tilt magnets being spaced apart from each other along said radial direction, and a pair of tilt coils arranged facing said paired tilt magnets, each of said tilt coils having an axis of winding wire direction corresponding to the tangential direction; said paired tilt magnets being provided to said movable block; said paired tilt coils being provided to said stationary block; and a back yoke being provided on the surface of said tilt magnet opposite to the surface thereof facing said tilt coil. 